1. Field of the Invention
The present invention relates generally to fluid-filled vibration damping devices exhibiting vibration damping effect on the basis of flows of non-compressible fluid filled therein. More particularly, the present invention is concerned with a fluid-filled vibration damping device that is capable of exhibiting an excellent vibration damping effect with respect to vibrations applied thereto in two directions, i.e., in an axial direction parallel to a central axis of the damping device and in a radial direction perpendicular to the central axis of the damping device, on the basis of the flows of the non-compressible fluid, and that is suitably adoptable as an engine mount for automotive vehicles, for example.
2. Description of the Related Art
A fluid-filled vibration damping device adapted to exhibit a vibration damping effect on the basis of flows of a non-compressible fluid filled therein is known as one type of a vibration damping device interposed between two members of a vibration system for elastically connecting the two members, or for mounting one of the two members of the vibration system on the other member in a vibration damping fashion. JP-B-63-61533 and JP-A-61-262244 disclose known examples of such a fluid-filled vibration damping device capable of exhibiting desired vibration damping effect with the help of the flows of the non-compressible fluid, with respect to input vibrations applied thereto in an axial direction parallel to a central axis of the damping device and a radial direction perpendicular to the central axis of the damping device.
The disclosed a fluid-filled vibration damping device includes (a) a first mounting member having a support shaft portion; (b) a second mounting member having a cylindrical portion, the first and second mounting members being disposed relative to each other such that the first mounting member is located on the side of one of axially opposite open ends of the cylindrical portion of the second mounting member with its support shaft portion axially inserted into the cylindrical portion of the second mounting member; (c) an elastic body elastically connecting the supporting shaft portion of the first mounting member and the cylindrical portion of the second mounting member so that an opening of one of axially opposite ends of the cylindrical portion of the second mounting member is fluid-tightly closed by the elastic body; (d) a primary fluid chamber partially defined by the elastic body and formed within the cylindrical portion of the second mounting member, while being filled with the non compressible fluid; (e) an auxiliary fluid chamber filled with the non-compressible fluid whose pressure changes relative to a pressure of the fluid within the primary fluid chamber upon application of an axial vibrational load between the first and second mounting members; (f) a first orifice passage for fluid communication between the primary and auxiliary fluid chambers; (g) a pair of working fluid chambers formed at respective circumferential portions of the elastic body opposed to each other in a diametric direction of the elastic body with the supporting shaft portion of the first mounting member interposed therebetween; and (h) a second orifice passage for fluid communication between the pair of working fluid chambers. When the axial vibrational load is applied between the first and second mounting members, the thus constructed vibration-damping device is able to exhibit vibration damping effect with respect to the axial vibrational load on the basis of flows or resonance of the fluid through the first orifice passage between the primary and auxiliary fluid chambers. When a vibrational load is applied to the vibration-damping device in the radial direction perpendicular to the central axis of the device (herein after referred to as a “radial vibrational load”), the vibration-damping device is able to exhibit a desired vibration damping effect on the basis of flows or resonance of the fluid flowing through the second orifice passage between the pair of working fluid chambers.
The disclosed fluid-filled vibration damping device may be adopted for use in a front-engine front-drive type automotive vehicle (hereinafter referred to as a “FF type vehicle as an engine mount for supporting an engine mounted transversely in the vehicle, for example. In this case, the fluid-filled vibration damping device is installed in position with its first mounting member being fixed to the power unit and with its second mounting member being fixed to the body, for thereby mounting the power unit on the body of the vehicle in a vibration damping fashion. Thus, the fluid-filled vibration-damping device is capable of exhibiting the desired vibration damping effects with respect to input vibrations in the vertical and longitudinal direction of the vehicle on the basis of the above-described resonance of the fluid.
For a vibration damping support of a power unit of the transversely mounted engine on the FF-type vehicle in an efficient and effective manner, the power unit is desirably supported in a vibration damping fashion by two engine mounts located on and fixed to laterally opposite sides of the power unit, at respective points located on a primary inertia axis of the power unit. Namely, it is preferable to support the power unit by the two engine mounts in an uncoupled vibration damping fashion or structure.
Recent tendency to reduce the volume of an engine room in an attempt to increase a volume of a passenger's room, or due to an increase in the number of various kinds of auxiliary devices housed in the engine room, inevitably causes a restriction or reduction of the space for installation of the engine mount. In particular, the transversely mounted engine of the FF-type vehicle is more likely to be placed on a tire housing of the vehicle due to its arrangement. Accordingly, the fixing point of the first mounting member of each of the engine mounts is located in a higher position of the power unit, so that a support position in which the engine mount supports the power unit in a vibration damping fashion is prone to be located above the primary inertia axis of the power unit in the vertical direction. For the above reasons, the conventional vibration-damping device used as the engine mount for supporting the power unit of the transversely mounted engine of FF-type vehicle is insufficient to exhibit a desired vibration damping characteristics and fails to exhibit an excellent vibration damping effect.
For installation on the tire housing, the engine mount is generally arranged such that a central axis of the first and second mounting members extend approximately in the vertical direction. The first mounting member is disposed on the side of the axially or vertically upper end of the second mounting member, and the axially or vertically lower end of the second mounting member is fixedly connected to the body of the vehicle. Therefore, a vibration input position to which a vibrational load of the power unit is applied to the vibration-damping device through the first mounting member, is prone to be spaced apart from the fixing portion in which the second mounting member is connected to the body of the vehicle in the vertically upward direction with a relatively large vertical distance therebetween. This may cause an increase in a moment acting to the fixing portion of the second mounting member to the body of the vehicle, when the vibrational load is applied to the engine mount through the first mounting member, thus deteriorating strength, bonding strength and durability of the first and second mounting members in their fixing portions to members of the vehicle.